.TH "seccomp_attr_set" 3 "21 September 2022" "paul@paul-moore.com" "libseccomp Documentation"
.\" //////////////////////////////////////////////////////////////////////////
.SH NAME
.\" //////////////////////////////////////////////////////////////////////////
seccomp_attr_set, seccomp_attr_get \- Manage the seccomp filter attributes
.\" //////////////////////////////////////////////////////////////////////////
.SH SYNOPSIS
.\" //////////////////////////////////////////////////////////////////////////
.nf
.B #include <seccomp.h>
.sp
.B typedef void * scmp_filter_ctx;
.B enum scmp_filter_attr;
.sp
.BI "int seccomp_attr_set(scmp_filter_ctx " ctx ","
.BI "                     enum scmp_filter_attr " attr ", uint32_t " value ");"
.BI "int seccomp_attr_get(scmp_filter_ctx " ctx ","
.BI "                     enum scmp_filter_attr " attr ", uint32_t *" value ");"
.sp
Link with \fI\-lseccomp\fP.
.fi
.\" //////////////////////////////////////////////////////////////////////////
.SH DESCRIPTION
.\" //////////////////////////////////////////////////////////////////////////
.P
The
.BR seccomp_attr_set ()
function sets the different seccomp filter attributes while the
.BR seccomp_attr_get ()
function fetches the filter attributes.  The seccomp filter attributes are
tunable values that affect how the library behaves when generating and loading
the seccomp filter into the kernel.  The attributes are reset to their default
values whenever the filter is initialized or reset via
.BR seccomp_init (3)
or
.BR seccomp_reset (3).
.P
The filter context
.I ctx
is the value returned by the call to
.BR seccomp_init (3).
.P
Valid
.I attr
values are as follows:
.TP
.B SCMP_FLTATR_ACT_DEFAULT
The default filter action as specified in the call to
.BR seccomp_init (3)
or
.BR seccomp_reset (3).
This attribute is read-only.
.TP
.B SCMP_FLTATR_ACT_BADARCH
The filter action taken when the loaded filter does not match the architecture
of the executing application.  Defaults to the
.B SCMP_ACT_KILL
action.
.TP
.B SCMP_FLTATR_CTL_NNP
A flag to specify if the NO_NEW_PRIVS functionality should be enabled before
loading the seccomp filter into the kernel.  Setting this to off
.RI ( value
== 0) results in no action, meaning that loading the seccomp filter into the
kernel will fail if CAP_SYS_ADMIN is missing and NO_NEW_PRIVS has not been
externally set.  Defaults to on
.RI ( value
== 1).
.TP
.B SCMP_FLTATR_CTL_TSYNC
A flag to specify if the kernel should attempt to synchronize the filters
across all threads on
.BR seccomp_load (3).
If the kernel is unable to synchronize all of the thread then the load
operation will fail.  This flag is only available on Linux Kernel 3.17 or
greater; attempting to enable this flag on earlier kernels will result in an
error being returned.  Defaults to off
.RI ( value
== 0).
.TP
.B SCMP_FLTATR_API_TSKIP
A flag to specify if libseccomp should allow filter rules to be created for
the -1 syscall.  The -1 syscall value can be used by tracer programs to skip
specific syscall invocations, see
.BR seccomp (2)
for more information.  Defaults to off
.RI ( value
== 0).
.TP
.B SCMP_FLTATR_CTL_LOG
A flag to specify if the kernel should log all filter actions taken except for
the
.BR SCMP_ACT_ALLOW
action. Defaults to off
.RI ( value
== 0).
.TP
.B SCMP_FLTATR_CTL_SSB
A flag to disable Speculative Store Bypass mitigations for this filter.
Defaults to off
.RI ( value
== 0).
.TP
.B SCMP_FLTATR_CTL_OPTIMIZE
A flag to specify the optimization level of the seccomp filter.  By default
libseccomp generates a set of sequential \'if\' statements for each rule in
the filter.
.BR seccomp_syscall_priority (3)
can be used to prioritize the order for the default cause.  The binary tree
optimization sorts by syscall numbers and generates consistent
.BR O(log\ n)
filter traversal for every rule in the filter.  The binary tree may be
advantageous for large filters.  Note that
.BR seccomp_syscall_priority (3)
is ignored when SCMP_FLTATR_CTL_OPTIMIZE == 2.
.RS
.P
The different optimization levels are described below:
.TP
.B 0
Reserved value, not currently used.
.TP
.B 1
Rules sorted by priority and complexity (DEFAULT).
.TP
.B 2
Binary tree sorted by syscall number.
.RE
.TP
.B SCMP_FLTATR_API_SYSRAWRC
A flag to specify if libseccomp should pass system error codes back to the
caller instead of the default -ECANCELED.  Defaults to off
.RI ( value
== 0).
.TP
.B SCMP_FLTATR_CTL_WAITKILL
A flag to specify if libseccomp should request wait killable semantics when
possible.  Defaults to off
.RI ( value
== 0).
.\" //////////////////////////////////////////////////////////////////////////
.SH RETURN VALUE
.\" //////////////////////////////////////////////////////////////////////////
Returns zero on success or one of the following error codes on
failure:
.TP
.B -EACCES
Setting the attribute with the given value is not allowed.
.TP
.B -EEXIST
The attribute does not exist.
.TP
.B -EINVAL
Invalid input, either the context or architecture token is invalid.
.TP
.B -EOPNOTSUPP
The library doesn't support the particular operation.
.\" //////////////////////////////////////////////////////////////////////////
.SH EXAMPLES
.\" //////////////////////////////////////////////////////////////////////////
.nf
#include <seccomp.h>

int main(int argc, char *argv[])
{
	int rc = \-1;
	scmp_filter_ctx ctx;

	ctx = seccomp_init(SCMP_ACT_ALLOW);
	if (ctx == NULL)
		goto out;

	/* ... */

	rc = seccomp_attr_set(ctx, SCMP_FLTATR_ACT_BADARCH, SCMP_ACT_TRAP);
	if (rc < 0)
		goto out;

	/* ... */

out:
	seccomp_release(ctx);
	return \-rc;
}
.fi
.\" //////////////////////////////////////////////////////////////////////////
.SH NOTES
.\" //////////////////////////////////////////////////////////////////////////
.P
While the seccomp filter can be generated independent of the kernel, kernel
support is required to load and enforce the seccomp filter generated by
libseccomp.
.P
The libseccomp project site, with more information and the source code
repository, can be found at https://github.com/seccomp/libseccomp.  This tool,
as well as the libseccomp library, is currently under development, please
report any bugs at the project site or directly to the author.
.\" //////////////////////////////////////////////////////////////////////////
.SH AUTHOR
.\" //////////////////////////////////////////////////////////////////////////
Paul Moore <paul@paul-moore.com>
.\" //////////////////////////////////////////////////////////////////////////
.SH SEE ALSO
.\" //////////////////////////////////////////////////////////////////////////
.BR seccomp_init (3),
.BR seccomp_reset (3),
.BR seccomp_load (3),
.BR seccomp (2)
